Common Mistakes
Graywater Systems
Use good design
Avoid common pitfalls and poor design choices by thoroughly educating yourself about common mistakes with Graywater system designs
Common Mistakes
Avoiding manually cleaned filters
High amounts of dissolved solids, nutrients and associated bacteria in graywater rapidly clog filters such that relying on manually cleaning a filter is NEVER recommended. Abandonment of greywater systems due to filter & maintenance failure is the inevitable situation occurring with manually cleaned filter systems. All successful filter systems are automatically self-cleaning and regardless tend to require the most troubleshooting of any part of the system.
Avoid Cheap Pumps not rated for wastewater
Pumps should be:
Rated to pass 3/4” solids
Pumps are different sizes (horsepower) depending on the distance and height you have to reach
Inline float switch attached to the pump activates pump as soon as basin fills with Graywater
submersible
Vortex impeller or similar technology approved for sewage effluent
Dirty water submersible pumps are designed to pump soft solids up to 1 1/2" or more in size with little to no filtration required before the pump
Include a check valve (alllows one-way flow only) to prevent Backflow into the basin.
A course mesh hair catch filter bag recommended be installed at the inlet into the basin, designed such that even after clogging it does not impede the passage of graywater into the basin.
Include Unions ( a plumbing coupling designed to be easily removable)to allow for easy removal and maintenance of the pump
Power for pump typically supplied by an existing plug-in 120 V GFCI outlet (cutting the plug off the end of the pump cord (for hard wiring) will void the pump warranty)
Electricity use of a 660 Watt pump (running for 1/2 hour per day in a typical 4-person household), would be an actual use of 450 Watts during operation, for a total daily power usage of 0.25 kilowatt hours which represents 0.6% of the average home power consumption.
Don’t store Graywater for more than 24 hrs
The high amounts of nutrients and suspended solids and bacteria in graywater rapidly multiply under storage to turn into noxious septic blackwater, which is why graywater is never stored for more than 24 hours. .
Don’t discharge graywater near natural waters
Potential environmental pollution can result if harmful chemicals in greywater enter the groundwater & surface water. Even naturally occurring nutrients in greywater can contaminate creeks and other surface water by contributing to algae growths that consume oxygen, which is why systems are designed to minimize contact, prevent ponding and runoff and contain graywater onsite. Releasing graywater in close proximity (within 100 ft) to streams, lakes, water wells, or drainage ways may inevitably lead to surface or drinking water contamination and is prohibited.
Photo Credit: Ned Harris 12/26/2012
Avoid small orifices with unfiltered graywater
Don’t distribute unfiltered grey water through perforated pipe, drip emitters or other small orifices, which will clog readily with the plentiful suspended solids in grey water. Other types of wastewater such as septic effluent are able to be successfully distributed through perforated pipe in leachfields because septic tanks are effective for removing suspended solids.
Dont expose graywater to the surface
Discharge greywater below the surface under a minimum 2″ cover of mulch, plastic shield, or stones so that its not accessible to people or pets. Theres never been a documented case of illness from graywater, but nevertheless all systems should be designed to avoid the possibility of contact or ingestion.
Dont connect potable water without an air gap or approved BFPD
Backflow prevention devices (BFPD) ensure water quality by preventing contamination of the potable (drinking) water supply due to back-pressure or back-siphonage of graywater into the municipal system. Local regulations vary as to acceptable backflow standards but generally speaking the Reduced pressure (RP) backflow device ( RP valve) is the most reliable backflow prevention device and can protect against both back- pressure and back-siphonage. Above ground installation is required with concrete stabilization and a minimum 12-inch gap between the relief valve and finished grade to allow the RP to discharge water when a back-siphon situation occurs. Backflow preventer devices are legally required to be inspected annually by a certified backflow inspector. Improper designs could create a cross connection where greywater could enter potable water pipes.
